1. Technical Field
The present invention relates to a method and arrangement for sensor diagnosis in an internal combustion engine. More particularly, the invention relates to a method and arrangement for diagnosing a pressure sensor used for detection of the pressure of fuel fed to an internal combustion engine.
2. Background Information
A fuel pump is often utilized for feeding the fuel to the engine of vehicles driven by a combustion engine. According to conventional techniques, the fuel pump is arranged in connection with the vehicle fuel tank, and functions to feed fuel from the tank at a sufficient flow rate and a suitable fuel pressure to the engine. In doing so, the fuel supplied to the engine can be provided during the various operating states of the engine.
Fuel pumps used with conventional, port-injected gasoline engines, i.e., engines with injection devices arranged in the intake passages of each engine cylinder, are intended to maintain a fuel pressure of about 0.3 to about 0.4 MPa, or about 45 to about 60 psi. In a direct injection (xe2x80x9cDIxe2x80x9d) engine, i.e., a DI Otto or piston type engine, each combustion chamber of the engine is arranged so that the fuel supplied can be highly concentrated around the spark plug in connection with combustion of the fuel. This arrangement or mode is commonly referred to as a xe2x80x9cstratifiedxe2x80x9d operation and allows during continuous running, for example, at a low or medium torque and/or engine speed, operation with a very lean air/fuel mixture. In particular, this type of arrangement allows the engine to run with a Lambda value (xcex) up to and above about xcex=3. By doing so, a reduction in fuel consumption by the engine is achieved.
The DI engine can also be operated in a xe2x80x9chomogeneousxe2x80x9d operation mode, with a substantially stoichiometric mixture ( i.e., a xcex value of about 1 to about 1.2), or a relatively rich mixture ( i.e., a xcex value of less than 1). This latter, rich operating mode normally exists in driving situations with relatively high torque and high speed of the engine.
Because fuel is injected in a very short time period during stratified operation in a DI engine (in contrast to conventional port-injected engines), a substantially higher fuel pressure is required for DI engines than for conventional engines. Therefore, in DI engines both a conventional fuel pump, arranged by the tank and operative to feed fuel at a pressure of about 0.3 to about 0.4 MPa, and a high-pressure pump, for feeding fuel to the electrically controlled injecting devices, or injectors at each cylinder, are used. The high-pressure pump typically operates at a pressure of about 5 to about 15 MPa. Thus, the fuel pressure can be varied as a function of the load, speed and operating range of the engine in question.
For controlling the pressure of the fuel supplied to each injector, a pressure sensor is used for detecting the current fuel pressure. With these pressure sensors, there is a requirement for monitoring the sensor in order to determine and indicate any malfunction of the sensor. Such a diagnosis could include a plausibility assessment. In a plausibility assessment, or xe2x80x9cout-of-rangexe2x80x9d diagnosis, a control unit is used to control fuel pressure if the pressure measured by the pressure sensor is higher than a predetermined highest possible value or lower than a predetermined lowest possible value. If the pressure is out of range, the sensor can be considered defective.
Although reliable in principle, this diagnosis still has problems. This assessment does provide a method or means of checking the pressure sensor for defects in those cases where the currently measured data actually lies within the expected range, i.e., when the measured data lies between the highest possible value and the lowest possible value.
The present invention provides an improved method and arrangement for diagnosis of a fuel pressure sensor in an automotive vehicle compared to known diagnosis methods as discussed above. This is achieved by a method and arrangement involving a fuel pump for feeding fuel under pressure to the engine. A sensor is provided for detecting the fuel pressure. The air/fuel mixture provided to the engine is controlled by performing an intentional modification of both the pressure and the time period in which fuel is injected to the engine. These modifications are selected in such a way that no change in the flow of fuel to the engine occurs. A check is then performed to determine if the modifications caused any unallowable deviation in the operating state of the engine. If so, a defective pressure sensor indication is given.
With the invention, a substantial advantage is achieved in relation to conventional systems. In contrast to conventional systems, the present invention allows a plausibility test that enables any deficiencies in the sensor to be detected even though the measured data falls within an expected or normal measurement range. This provides a higher or more reliable diagnosis method.
In one embodiment of the invention, the check further includes determining whether the modifications result in any unallowable deviation in the control of feeding the air/fuel mixture to the engine. In one embodiment of the invention, the check further determines whether the pressure sensor signal falls outside of a predetermined range, or highest and lowest conceivable measurement value. In such an instance where the signal is out of range, the sensor is considered defective. In another embodiment of the invention, a check is performed to determine if a suitable operating mode of the engine exists before performing the modifications. In one embodiment of the invention, the indication of the defective sensor includes the actuation of an alarm such as a warning light.
An embodiment of the invention may also include a high pressure pump for feeding fuel to the engine. The pressure sensor is preferably arranged downstream of the high pressure pump.